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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  130 


EXPERIMENTS  WITH  REPELLENTS 
AGAINST    THE    CORN    ROOT- 
APHIS,  1905  AND  1906 


BY  STEPHEN  A.  FORBES 
STATE  ENTOMOLOGIST 


URBANA,   ILLINOIS,   DECEMBER,   1908 


SUMMARY  OF  BULLETIN  No.  130 

1.  Thirty  minutes'  soaking  of  seed-corn  in  kerosene  before  planting,  injured 
seed   but   protected   plants   against   root-aphis    in   preliminary    field    experiment 
made  in  1905.  Pages  4-5 

2.  Summer   plot-plantings   made   in    1905,    with    seed   treated   with   kerosene, 
kerosene   emulsion,   coal-tar   water,   or   turpentine,    showed   no   injury   after   a 
moderate  use  of  kerosene  and  coal-tar  water.     Results  with  kerosene  emulsion 
and  with  turpentine  were  conflicting.  Pages  5~8 

3.  Indoor  pot-plantings  in   1906  showed  no  injury  after  a  moderate  use  of 
kerosene,  oil  of  lemon,  carbolic  acid,   formalin,  lysol,  chlorid  of  lime,  carbon 
bisulphid,    tobacco    water,    or    camphor.     Soaking   in   common    alcohol    for   30 
minutes  or  in  wood  alcohol  for  20  minutes,  injured  the  seed.    Tests  made  of 
various  other  substances.  Pages  9~15 

4.  Extensive  field  experiments  were  made  in  1906  with  minimum  quantities 
of  oil  of  lemon,  kerosene,  formalin,  and  carbolic  acid  applied  to  seed  just  before 
planting.     Examination  six  weeks  after  planting  showed  average  diminution  of 
number  of  root-lice,  and  of  hills  infested  by  them,  as  follows :  oil  of  lemon, 
76  percent ;  kerosene,   57  percent ;    formalin,  49  percent ;   carbolic   acid,  8  per- 
cent.    Ten  weeks  after  planting,  corn  in  the  experimental  plots  averaged  72  per- 
cent taller  than  in  checks.    Examined  19  weeks  after  planting,  applications  made 
to  the  seed  were  found  to  have  increased  the  number  of  ear-bearing  stalks  to 
the  acre  as   follows:   oil   of   lemon,    1159-;   carbolic   acid,   945;    formalin,   742; 
kerosene,  274.  Pages  15-23 

5.  The  increase  in  root-lice  in  the  field  was  seven-fold  in  twenty-three  days — 
equal  to  nearly  3  millions  to  1  between  April  1  and  October  1.  Page  21 

6.  In  a  small  special  test,  made  by  planting  a  few  hills  of  corn  close  around 
nests  of  ants  in  the  field,  kerosene  and  carbolic  acid  kept  the  insects  away  from 
the  corn,  but  oil  of  lemon,  formalin,  and  several  other  substances  tested,  were 
without  effect.  Pages  24-26 

7.  General  procedure  recommended  as  protection  to  corn  against  root-aphis 

Pages  26-28 


EXPERIMENTS  WITH  REPELLENTS  AGAINST 

THE  CORN    ROOT-APHIS, 

1905  AND  1906 

BY  STEPHEN  A.  FORBES,  STATE  ENTOMOLOGIST 

The  corn  root-aphis,  a  minute,  bluish  green,  sluggish,  soft-bodied 
insect  found  on  the  roots  of  corn,  is  one  of  the  most  destructive  and 
dangerous  insect  pests  of  the  corn  plant.  Beginning  as  soon  as  the 
kernel  sprouts  to  suck  the  sap  from  the  young  roots,  it  may  continue 
its  injury  without  interruption  until  frost,  unless  the  infested  plant 
in  the  meantime  perishes.  It  has  an  enormous  power  of  multiplication, 
producing,  under  favorable  circumstances,  as  many  as  sixteen  gc aera- 
tions in  a  season,  and  it  is  capable  of  spreading  from  field  to  field 
rapidly  on  the  wing,  many  of  each  generation,  except  the  first  of  the 
year,  having  the  power  of  flight. 

Altho  a  peculiarly  sluggish  and  stupid  insect,  wholly  unable  to 
make  its  own  way  unaided,  it  has  always  in  its  service  one  of  the  most 
capable,  abundant,  active,  and  persistent  of  our  common  insect  species. 
This  is  the  so-called  corn-field  ant  (Lasius  alienus  americanus) ,  in 
whose  charge  the  corn  root-aphis  is  usually  found,  and  by  which  its 
eggs,  laid  in  fall,  are  carried  thru  the  winter.  This  corn-field  ant 
has  no  power  of  injuring  the  corn  directly,  except  as  it  may  occasion- 
ally, or  under  peculiar  circumstances,  devour  the  softened  kernel  in 
the  earth,  and  the  root-aphis,  left  to  itself,  can  not  even  get  access  to  its 
food  in  numbers  to  do  any  noticeable  harm ;  but  the  two  in  partnership 
check  the  growth  of  the  plants,  and  even  kill  outright  whole  fields  of 
corn,  the  aphis  making  the  destructive  attack,  and  the  ant  protecting, 
transporting,  and  guarding  the  aphis,  and  collecting,  preserving,  and 
hatching  its  eggs. 

The  practical  control  of  this  pair  of  insects  is  especially  important 
because  the  injury  done  to  corn,  already  very  heavy,  is  sure  to  increase 
with  time.  The  more  generally  and  continuously  corn  is  grown,  and 
the  more  the  soil  deteriorates  under  continuous  cropping,  the  greater 
this  aphis  injury  must  become.  It  is  hence  most  serious  and  threaten- 
ing in  those  very  parts  of  our  area  best  adapted  to  corn,  and  is  much  the 
greatest  now  in  Illinois  in  the  central  part  of  the  state,  where  corn  is 
the  principal  crop. 

Neither  of  these  insects  is  subject,  so  far  as  known,  to  destruction 
by  parasites  or  by  contagious  diseases,  the  principal  natural  checks  on 
the  multiplication  of  most  other  injurious  species.  About  the  only 
natural  agency  which  can  be  depended  on  to  reduce  the  numbers  of 
the  corn  root-aphis  is  a  long-continued  soaking  of  the  ground  by  fre- 
quent heavy  rains,  especially  if  these  come  in  a  slow,  cool  spring.  The 
very  wet  spring  of  1907,  for  example,  seems  to  have  had  the  effect  to 


4  BULLETIN  No.  130  [December, 

drown  out  the  root-lice  and  also,  to  some  extent,  the  maggotlike  young 
of  the  ants  under  ground ;  and  some  fields  heavily  enough  infested  in 
April  and  early  May  of  that  year  to  make  a  profitable  crop  very  un- 
likely, were  completely  cleared  of  root-lice  by  the  beginning  of  June, 
and  contained  unusually  few  ants. 

Our  later  work  on  the  ant-aphis  problem  has  been  done  mainly  on 
two  lines.  We  have  attempted  to  test,  by  field  experiments,  the  value 
of  a  repeated  deep  and  thoro  stirring  of  the  soil  previous  to  planting, 
and  we  have  experimented  with  offensive  applications  to  the  seed,  of  a 
kind  to  last  a  considerable  time  in  the  ground,  and  to  keep  the  ants, 
and  consequently  the  aphids,  out  of  the  hills  as  long  as  possible  while 
the  plant  was  still  young  and  especially  sensitive  to  injury.  Experi- 
ments of  the  first  class  were  reported  in  Bulletin  104  of  the  Agricul- 
tural Experiment  Station  published  in  October,  1905,  and  again  in  the 
Twenty-fourth  Report  of-  the  State  Entomologist,  pages  8  to  29;  but 
those  with  repellents  applied  to  the  seed  in  1905-06  are  here  fully  re- 
ported for  the  first  time. 

REPELLENT  APPLICATIONS  TO  THE  SEED 

My  attention  was  first  called  to  the  fact  that  applications  to  the 
seed  might  serve  to  protect  young  corn  against  root-louse  attack  by 
statements  occasionally  made  by  farmers  who  had  treated  their  seed- 
corn  with  kerosene  or  turpentine  just  before  planting.*  Having,  I 
must  confess,  very  little  faith  in  this  treatment,  I  nevertheless  directed 
an  assistant,  Mr.  E.  O.  G.  Kelly,  in  charge  of  my  field  work  in  1905, 
to  test  the  effect  of  kerosene  used  in  this  way,  and  as  part  of  a  general 
field  experiment  for  the  protection  of  corn  against  aphis  injury,  he 
planted  a  small  plot  in  an  experimental  field  with  seed  which  had  been 
soaked  in  kerosene  for  half  an  hour. 

The  effect  of  this  treatment  was  a  double  surprise  to  us.  In  the 
first  place,  only  about  half  as  much  of  the  corn  grew  as  in  other  ex- 
periments made  in  the  same  field  with  seed  from  the  same  lot,  serving, 
consequently,  as  checks  on  this ;  the  other  half  swelled  up  with  the 
moisture  absorbed,  but  never  sprouted.  Furthermore,  germination 
was  delayed,  growth  of  the  young  corn  was  slow  at  first,  and  many  of 
the  plants  were  dwarfed  and  crippled,  the  growing  tip  or  plumule  of 
the  plant  making  its  way  with  great  difficulty  out  of  the  inclosing 
sheath  (the  coleophyl)  which  protects  it  as  it  grows  upward  thru 
the  earth.  In  the  second  place,  altho  the  field  of  corn  of  which  this 
planting  was  a  part  was  heavily  infested  and  noticeably  injured  by  the 
corn  root-aphis,  this  special  plot,  when  examined  some  weeks  after 
planting,  was  found  to  be  almost  wholly  free  from  the  aphis,  and  to 
contain  but  few  ants ;  and  at  husking  time  its  yield  equaled  in  quan- 
tity and  excelled  in  quality  that  of  like  areas  in  other  parts  of  the  same 
field.  The  treatment  of  the  seed  had  evidently  so  repelled  the  ants 


*See   especially  my   address  on  the  corn  root-aphis   in    the    Tenth    Report   of   the    Illinois 
Farmers'   Institute,   p.   49. 


1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  5 

and  aphids  that  protection  from  their  injury  had  more  than  compen- 
sated for  the  original  poor  stand.  It  thus  became  our  problem  so  to 
modify  this  treatment  as  to  get  the  beneficial  result  without  risk  of 
the  injury. 

It  was  evident  enough  that  kerosene  merely  applied  to  the  seed 
could  act  only  by  reason  of  its  persistent  odor — peculiarly  offensive  to 
ants — and  it  seemed  quite  probable  that  corn  might  be  so  treated  with 
this  or  some  other  strong-smelling  substance  that  ants  would  be  kept 
out  of  the  hills  for  a  considerable  time  and  that  the  seed  would  not  be 
injured.  As  a  test  of  substances  possibly  useful  for  this  purpose,  a 
long  series  of  experimental  plantings  was  made,  from  June  to  August, 
1905,  and  from  February  to  July,  1906,  in  the  field,  at  Urbana,  and  in 
the  insectary  connected  with  my  office  there,  and  a  careful  record  was 
kept  of  the  percentage  of  kernels  germinating  in  each  planting,  and  of 
the  condition  of  the  corn  plants  for  several  days  after  they  appeared 
above  ground.  The  substances  thus  tested  as  to  their  effects  on  corn 
were  kerosene,  kerosene  emulsion,  crude  petroleum,  turpentine,  car- 
bolic acid,  formalin,  oil  of  lemon,  oil  of  wintergreen,  oil  of  cloves,  oil 
of  sassafras,  wood  alcohol,  common  alcohol,  coal-tar,  coal-tar  water, 
carbon  bisulphid,  chlorid  of  lime,  kainit,  flowers  of  sulphur,  lime,  salt, 
various  compound  solutions  of  sulphur,  lime,  and  salt,  and  of  sulphur, 
lime,  and  blue  vitriol,  copper  sulphate,  iron  sulphate,  mustard,  cam- 
phor, musk,  lysol,  tobacco-water,  the  proprietary  insecticides  known 
as  "Scalecide,"  "Con  Sol,"  "Calcothion,"  and  "Fruitolin,"  and  the  so- 
called  "Rex  Dip." 

PLOT  EXPERIMENTS,  1905 

For  this  purpose  the  use  of  a  plot  of  ground  was  obtained  in  June, 
1905,  on  the  farm  of  the  Experiment  Station  at  Urbana,  on  which  the 
corn  was  planted  in  rows  by  hand,  usually  two  grains  to  the  hill. 
Fifteen  thousand  five  hundred  kernels  were  planted  in  this  plot,  5750 
of  them  after  treatment  with  kerosene,  2050  with  kerosene  emulsion, 
2000  with  tar-water,  3650  with  turpentine,  and  2050,  with  no  special 
application,  serving  as  checks.  The  principal  plantings  were  those 
made  June  15,  of  1500  kernels,  and  June  28,  of  12,500  kernels. 
Smaller  additional  plantings,  varying  from  50  to  1000  kernels,  were 
made  June  29  and  30.  July  18  and  21,  and  August  9. 

The  results  of  the  planting  of  June  15  were  determined  by  an  in- 
spection June  26,  and  those  of  June  28  were  determined  July  20 — the 
first,  eleven  days  after  planting,  and  the  second  after  twenty-two  days. 
The  weather  of  these  two  intervals  differed1  materially,  that  between 
June  15  and  June  26  being  rather  dry,  and  that  between  June  28  and 
July  20  decidedly  wet — a  fact  to  be  borne  in  mind  at  some  points  in 
comparing  the  two  series  of  experiments.  The  ground  must  have  been 
fairly  moist,  however,  June  15,  since  a  rain  of  1.05  inches  had  fallen 
on  the  10th,  but  the  only  rain  to  fall  during  the  eleven  days  following 
June  15  was  .06  of  an  inch  on  the  20th.  Between  the  28th  of  June 
and  the  20th  of  July,  on  the  other  hand,  rain  fell  on  sixteen  days,  to 


6  BULLETIN  No.  130  [December, 

the  total  amount  of  5.34  inches — that  of  one  day,  July  5,  amounting 
to   1.44  inches. 

Treatment  of  seed  with  kerosene. — The  seed-corn  experiment  with 
kerosene  was  so  varied  as  to  bring  into  comparison  the  results  of  sim- 
ply dipping  the  seed  and  planting  immediately  afterwards,  and  of 
soaking  it  for  5  minutes,  10  minutes,  20  minutes,  and  30  minutes,  and 
for  11  days,  20  days,  and  41  days.  Tests  were  likewise  made  of  the 
effect  of  first  soaking  the  seed  in  water  before  putting  it  into  kerosene. 

The  checks  to  these  experiments — 2050  kernels  which  were  planted 
in  ten  lots  of  50  to  500  kernels  each  at  several  dates  between  June  15 
and  July  21 — germinated  in  ratios  ranging  from  83  to  96  percent,  with 
an  average  of  89 ;  and  with  this  average,  of  course,  the  germination 
ratios  of  the  various  experiments  are  to  be  compared. 

Eight  experimental  lots,  containing  2225  kernels  in  all,  received 
the  simplest  treatment — a  mere  dipping  in  kerosene  immediately  before 
planting.  The  ratios  of  germination  for  seven  of  these  lots  varied 
from  84  to  97,  with  an  average  of  91.  The  eighth  lot,  of  only  50  ker- 
nels planted  in  earth  kept  continuously  moist,  gave  a  germination  ratio 
of  62  percent,  and  including  this  the  average  for  the  series  is  87.6. 
It  may  fairly  be  said,  consequently,  that  injury  by  this  treatment  was 
practically  imperceptible,  but  that  a  suspicion  is  created  of  possible 
damage  to  the  seed  if  the  weather  is  continuously  wet  after  planting. 

Eight  lots  of  seed,  numbering  2225  kernels  in  all,  were  soaked  in 
kerosene  for  5  minutes  just  before  planting.  Here  also  no  perceptible 
damage  was  done  to  the  seed,  the  germination  ratio  amounting  to  88.8, 
to  be  compared  with  89  for  the  checks. 

Of  eleven  additional  lots,  averaging  100  kernels  each,  soaked  in 
kerosene  for  periods  varying  from  10  to  30  minutes,  85.2  percent  grew, 
the  ratios  ranging  from  78  to  96.  We  begin  to  see  here  evidences  of 
slight  but  obvious  injury  to  the  seed  as  a  consequence  of  the  treatment. 
It  is  nevertheless  puzzling  to  find  that  89  kernels  grew  out  of  100  ker- 
nels soaked  for  11  days,  and  that  86  percent  of  50  kernels  soaked  for 
20  days  and  80  percent  of  the  same  number  soaked  for  41  days,  also 
grew. 

In  many  of  these  kerosene  experiments,  even  tho  the  kernels 
sprouted  eventually  and  plants  appeared  above  ground,  the  germina- 
tion was  much  retarded  and  the  plants  were  more  or  less  distorted  and 
deformed — an  effect  returned  to  on  a  later  page  of  this  article. 

Kerosene  emulsion. — For  some  obscure  reason  the  result  of  the 
treatment  of  400  kernels  with  kerosene  emulsion  June  15,  was  very 
much  less  favorable  than  that  of  1500  kernels  planted  June  28.  In 
the  first  experiments  the  seed  was  soaked  for  30  minutes  in  emulsion 
diluted  to  contain  10  per  cent,  20  percent,  40  percent,  and  50  percent 
of  kerosene,  with  the  effect  to  give  a  germination  ratio,  eleven  days 
after  planting,  of  46  percent  for  the  first,  76  for  the  second,  63  for  the 
third,  and  57  for  the  fourth  of  these  lots,  or  an  average  of  60.5  percent 
to  grow  from  these  plantings.  June  28,  emulsions  were  used  contain- 
ing 10,  20,  and  40  percent  of  kerosene,  in  which  corn  was  soaked  for 
30  minutes,  each  of  three  lots  containing  500  kernels.  The  percent- 


1908] 


REPELLENTS  AGAINST  CORN  ROOT -APHIS 


ages  to  grow  varied  from  91.6  to  95.8,  with  an  average  of  93.  I  am 
unable  to  explain  these  discrepancies,  and  consequently  can  not  attach 
any  especial  importance  to  these  experiments  with  kerosene  emulsion. 

Turpentine. — A  like  discrepancy  appears  in  the  turpentine  experi- 
ments, four  plantings  for  which  were  made  June  15,  and  six  plantings 
June  28.  The  first,  of  100  kernels  each,  averaged  56^  percent  to  grow, 
and  the  second,  of  500  kernels  each,  averaged  88  percent.  In  the  plant- 
ings of  100  kernels  made  June  15  immediately  after  dipping  in  turpen- 
tine, 28  percent  grew;' while  of  another  hundred  soaked  in  turpentine 
for  5  minutes,  76  percent  grew.  Of  a  third  lot,  soaked  for  10  minutes, 
95  percent  grew ;  and  of  the  last  lot,  soaked  for  30  minutes,  but  27 
percent  grew.  These  variations  are  so  unaccountable  and  confusing 
as  to  vitiate  this  experiment. 

On  the  other  hand,  the  results  of  the  six  plantings  of  June  28 
varied  only  from  85  to  90  percent,  and  these  results  may  be  fairly 
accepted.  -  Of  500  kernels  dipped  in  turpentine  and  planted  at  once, 
90^prcent  grew ;  of  those  soaked  for  5  minutes  before  planting,  88 
percent  grew ;  and  of  those  soaked  for  20  minutes,  90  percent  grew. 
Of  another  lot  of  500  kernels,  soaked  first  in  water  for  10  minutes  and 
then  merely  dipped  in  turpentine,  90  percent  grew ;  of  a  second  lot 
treated  in  the  same  manner  except  that  they  were  soaked  for  5  minutes 
in  turpentine,  85  percent  grew ;  and  the  same  ratio  was  obtained  from 
a  third  lot  similarly  treated  except  that  the  kernels  were  soaked  for 
20  minutes  in  water.  This  treatment  with  turpentine  may  be  said, 
on  the  whole,  to  have  been  apparently  without  injurious  effect,  since 
the  check  plantings  of  this  date  gave  a  germination  average  of  89  per- 
cent, while  the  later  plantings  with  turpentine  averaged  88  percent 
to  grow. 

Tar-ivater. — Two  thousand  kernels  were  planted  June  28,  after 
treatment  with  coal-tar  water  obtained  from  the  bottom  of  a  gas  tank, 
or  from  the  top  of  a  tank  of  coal-tar,  at  the  gas  works.  One  thousand 
of  these  kernels,  merely  dipped  in  the  tar-water,  gave  a  germination 
ratio  of  94  percent,  and  of  another  thousand  soaked  in  it  for  5  minutes, 
88  percent  grew. 

The  principal  data  of  the  foregoing  discussion  are  summarized  in 
the  following  table. 

PLOT  EXPERIMENTS  WITH   REPELLENTS,   1905 


No  Treatment  of  Seed.     Check  Plots 


Date 

Treatment 

No.  of  kernels 

Percent  to  grow 

June  15 
"      28 
"     29 
July  21 

None             

200 
1500 
200 
150 

88 
89 
83 
95 

•  < 

<• 

Gener 

al  average  of  checks  

89 

BULLETIN  No.  130 
Seed  treated  with  Pure  Kerosene 


[December, 


Date 

Time  in  kerosene 

No.  of  kernels 

Percent  to  grow 

June  15 
28 
15 
28 
28 
15 
15 
15 
28 
30 
July  18 
Aug.    9 

Dipped  

100 
1000 
100 
1000 
1000 
100 
100 
100 
500 
100 
50 
50 

95 
97 
88 
94 
91 
85 
87 
82 
81 
89 
86 
80 

5  minutes.     Dry  

"          '          Wet  

10           '           Dry  

20          '             "     

30          '             "     

30          '           Wet  

11  days   

20     "      

41     "    

General  average  of  kerosene  treatmen 

ts  

88 

Seed  treated  with  Kerosene  Emulsion 

Date 

Percent 
kerosene 

Time  in  emulsion 

No.  of  kernels 

Percent  to  grow 

June  15 
IS 
15 
15 

28 
28 
28 

10 
20 
40 
SO 
10 
20 
40 

30  minutes  

100 
100 
100 
100 
500 
500 
500 

46 

76 
63 
57    60.5 

30        '        

30        '         

30        '        

30        '         

92 
92 
96    93^ 

30        '        
30 

Seed  treated  with  Turpentine 

Date 

Time  in  turpentine 

No.  of  kernels 

Percent  to  grow 

June  15 
15 
15 
15 

28 
28 
28 
28 
28 
28 

Dipped.  .  . 

100 
100 
100 
100 
500 
500 
500 
500 
500 
500 

28 
76 
95 
27    56.5 

5  minutes  

10      "        

30      "        

Dipped.     Di 
W 
5  minutes. 
5 
20 
20 

"V      . 

90 
90 

88 
85 
90 
85    88 

et  

Dry   . 

Wet  

Dry  . 

Wet  

Seed  treated  with  Coal-tar  Water 


Date 

Time  in  tar-water 

No.  of  kernels 

Percent  to  grow 

June  28 

Dipped.  . 

1000 

94 

"     28 

5  minutes  

1000 

88 

1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  9 

POT  EXPERIMENTS,  1906 

In  all  the  experiments  of  1906,  Learning  seed-corn  of  excellent 
quality  was  planted,  at  a  depth  of  an  inch,  in  good  black  soil  contained 
in  ordinary  earthen  flower-pots  seven  inches  across,  and  kept  in  the 
insectary  of  my  office  building  at  Urbana.  Temperature  and  moisture 
conditions,  being  under  strict  control,  were  made  as  nearly  those  of 
a  normal  spring  as  possible.  Thirty-five  check  lots  of  50  kernels  each 
(1750  kernels  in  all)  were  planted  with  untreated  seed  in  the  course  of 
these  experiments.  Sixteen  hundred  and  eighty  of  these  kernels  ger- 
minated, and  this  germination  ratio  (96  percent)  may  be  used  for  com- 
parison in  determining  the  effect  of  our  various  applications  to  the 
seed. 

Kerosene. — Kerosene  was  used  in  two  ways  in  these  experiments : 
(1)  by  mixing  it  thoroly  with  the  seed  in  quantities  varying  from  l/(> 
of  a  fluid  ounce  to  3^  ounces  for  each  gallon  of  corn;  and  (2)  by 
putting  the  seed  into  kerosene  and  soaking  it  there,  previous  to  plant- 
ing, for  periods  varying  from  10  minutes  to  19  hours.  The  main 
results  of  these  various  experiments  were  as  follows : 

Of  800  kernels  planted  after  stirring  in  kerosene  thoroly,  at  rates 
varying  from  ^  of  an  ounce  to  2  ounces  for  each  gallon  of  corn,  98 
percent  germinated,  and  only  2  of  the  plants  showed  any  trace  of 
injury.  Fifty  kernels  of  this  lot,  treated  at  the  rate  of  2  ounces  of 
kerosene  to  the  gallon,  all  sprouted,  and  none  of  these  plants  were  in- 
jured. Furthermore,  of  200  kernels  treated  with  kerosene  at  the  rate 
of  2}/$  to  3}/3  ounces  to  the  gallon  of  corn,  92  percent  germinated, 
and  only  3  plants  gave  any  appearance  of  injury.  It  would  naturally 
be  inferred  from  this  experiment  that  at  least  an  ounce  (two  table- 
spoonfuls)  of  kerosene  to  the  gallon  of  corn  might  be  safely  used 
under  conditions  as  favorable  as  those  in  our  management,  but  we 
shall  later  find  evidence,  in  the  outcome  of  a  field  experiment  made 
the  following  spring,  that  only  half  this  amount  injured  corn  slightly, 
but  still  appreciably,  under  the  weather  conditions  of  1906. 

Soaking  the  corn  in  kerosene  for  10-  to  20-  minute  periods,  200 
kernels  in  each  experiment,  gave  a  germination  ratio  of  88  percent  for 
the  first  and  93  percent  for  the  second,  but  with  the  appearance  of 
injury  to  77  percent  of  the  plants  in  the  10-minute  lot  and  of  80  per- 
cent in  the  20-minute  lot.  Furthermore,  the  plants  which  grew,  aver- 
aged only  2^4  inches  high  fifteen  days  after  planting,  while  100  plants 
from  untreated  seed  averaged  6^/3  inches.  The  corn  would  perhaps 
have  outgrown  this  backset,  and  might  have  made  a  crop,  if  planted 
out-of-doors,  better  than  the  average  in  the  field,  provided  that  the 
latter  was  injuriously  infested  by  the  corn  root-aphis. 

Soaking  seed  in  kerosene  for  periods  varying  from  4  hours  to  19 
hours  gave  variable  results,  as  reported  by  Mr.  Kelly.  Only  1  out 
of  50  grains  (2  percent)  soaked  for  4  hours  had  sprouted  at  the  end 
of  thirteen  days,  while  164  kernels  out  of  200  (82  percent)  which  had 
been  soaked  for  16  hours  before  planting,  appeared  above  ground 


10  BULLETIN  No.  130  [December, 

within  six  days,  92  percent  of  the  plants  finally  showing  more  or  less 
injury.  On  the  other  hand,  but  3  out  of  100  kernels  soaked  for  19 
hours  in  kerosene  were  in  condition  to  grow,  and  all  the  plants  from 
these  3  were  injured. 

Perplexing  discrepancies  of  this  sort  were  of  rather  frequent  oc- 
currence in  these  experiments,  and  showed  that  one  must  apply  the 
results  with  caution,  keeping  well  within  the- limits  of  variation.  In 
view  of  the  observed  effect  of  an  overdose  of  kerosene  on  the  young 
plant,  as  described  in  the  earlier  part  of  this  article,  it  is  important 
to  note  that  no  dwarfing  or  distortion  of  the  corn  plants  was  seen 
in  any  of  these  experiments. 

Crude  Petroleum. — A  series  of  tests  made  with  600'  kernels  of 
corn  by  soaking  them  in  crude  petroleum  for  various  periods  ranging 
from  5  minutes  to  74  hours,  gave  us  reason  to  believe  that  this  sub- 
stance was  too  dangerous  to  be  used  in  this  way.  No  experiments 
were  made,  however,  with  the  mere  mixture  of  minimum  quantities 
of  petroleum  with  a  gallon  of  corn.  The  same  variable  and  discrepant 
results  were  reported  here  as  in  the  experiments  with  kerosene,  14 
kernels  growing  out  of  50,  for  example,  which  had  been  soaked  for 
30  minutes,  and  46  out  of  50  which  had  been  soaked  for  19  hours. 
After  5  minutes'  soaking,  only  42  kernels  grew  out  of  50  planted,  and 
8  of  the  plants  which  appeared  were  injured. 

Oil  of  Lemon. — A  good  quality  of  oil  of  lemon,*  as  obtained  at  a 
local  wholesale  drug-store,  was  used  in  solution  with  ordinary  alcohol 
at  strengths  of  1  part  in  10  or  1  part  in  3  of  the  oil  to  the  alcohol.  The 
seed  was  soaked  in  these  mixtures  for  periods  varying  from  5  minutes 
to  an  hour.  Two  plantings  were  made  with  kernels  treated  by  stirring 
3  ounces  of  the  10  percent  solution  thoroly  into  a  gallon  of  the  seed. 
Of  450  kernels  treated  in  the  various  ways  described,  95  percent  ger- 
minated with  virtually  no  injury  to  the  plants. 

The  only  damage  done  to  the  seed  in  experiments  with  this  mixture 
of  lemon  oil  and  alcohol  appeared  in  two  lots  of  50  kernels  each 
soaked  in  the  10  percent  solution,  one  of  them  for  20  minutes  and 
the  other  for  19  hours.  In  the  first  of  these  lots  16  kernels,  and  in 
the  second  lot  21  kernels,  failed  to  grow.  It  was  a  perplexing  fact 
that  serious  injury  to  the  seed  was  thus  reported  by  Mr.  Kelly  to 
have  followed  the  use  of  a  10  percent  solution  for  20  minutes,  while 
no  harm  resulted  from  a  10  percent  solution  applied  for  30  minutes 
or  for  an  hour,  or  from  a  33*  percent  solution  applied  for  20  minutes 
or  for  30  minutes.  It  appeared  safe  to  conclude,  however,  that  a  10 
percent  solution  used  merely  to  moisten  the  seed,  say,  at  the  rate  of 
3  ounces  to  the  gallon  of  corn,  might  be  applied  without  risk  of  injury 
to  the  seed ;  and  our  field  experiments  were  made,  later  in  the  season, 
on  this  basis. 

Other  vegetable  oils. — Oil  of  wintergreen,  oil  of  cloves,  and  oil 
of  sassafras  were  tested,  each  with  400  kernels,  divided  into  eight 

*The  brand  and  manufacturer  of  this  sample  could  not  be  learned  later,  when  it  became 
important  to  know  just  how  the  results  of  these  experiments  were  obtained. 


1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  11 

experiments.  All  proved  to  be  too  frequently  injurious  to  the  seed 
to  make  it  safe  to  trust  to  them — the  oil  of  cloves  the  most  injurious 
and  the  oil  of  wintergreen  the  least  so.  Solutions  of  less  than  10 
percent  strength  were  not  used,  however,  and  no  trial  was  made  of 
any  milder  form  of  application  than  soaking  the  seed  for  5  minutes  in 
an  alcoholic  solution  of  the  oil.  It  is  possible,  consequently,  that  a  sim- 
ple stirring  into  the  seed  of  minimum  quantities  of  a  5  or  10  percent 
solution,  as  in  the  case  of  the  oil  of  lemon,  might  have  been  harm- 
less— excepting,  however,  the  oil  of  cloves,  which  killed  from  44  to 
100  percent  of  the  kernels  in  each  experiment. 

Carbolic  Acid. — The  action  of  carbolic  acid  was  tested  by  soaking 
seed-corn  from  5  to  30  minutes  in  solutions  of  the  commercial  acid 
in  water,  varying  in  strength  from  2  to  30  percent.  No  injury  was 
done  by  either  2  or  5  percent  solutions  applied  to  lots  of  200  kernels 
each  for  5,  10,  20,  or  30  minutes,  but  the  10  and  30  percent  solutions 
killed  virtually  all  the  seed  even  when  applied  for  only  5  minutes.  In 
our  subsequent  field  experiments  a  3  percent  solution  only  was  used, 
and  then  at  the  rate  of  3  ounces  of  the  solution  to  a  gallon  of  corn. 

Formalin. — A  few  experiments  made  with  formaldehyde,  in  water 
solutions  of  4  percent,  25  percent,  and  50  percent,  showed  that  at  4 
percent  this  substance  was  harmless  to  seed-corn  soaked  in  it  for 
any  period  between  5  minutes  and  half  an  hour.  Two  hundred  ker- 
nels thus  treated  gave  a  germination  ratio  of  94  percent.  The  plants 
which  grew,  on  the  other  hand,  averaged  only  4^4  inches  at  a  time 
when  the  single  check  of  50  plants  averaged  6  inches.  The  higher 
strengths-  mentioned1  were  both  extremely  injurious,  the  25  percent 
mixture  killing  from  one 'fourth  to  four  fifths  of  the  seed,  according 
to  the  period  of  use,  and  the  50  percent  mixture,  applied  for  half  an 
hour,  killing  it  all. 

The  Alcohols. — To  distinguish  between  the  effects  of  alcohol  and 
oils  in  some  of  the  above  mixtures,  200  kernels  were  soaked  in  com- 
mon alcohol  for  periods  ranging  from  5  minutes  to  half  an  hour, 
and  200  more  in  wood  alcohol  from  5  minutes  to  an  hour,  with  the 
result  that  no  injury  was  done  except  by  the  longer  periods  of  treat- 
ment. From  98  to  100  percent  of  the  grains  grew  after  soaking  10 
or  20  minutes  in  ordinary  alcohol,  but  only  66  percent  after  30  minutes' 
treatment ;  and  95  percent  grew  after  5  or  10  minutes  in  wood  alcohol, 
but  only  74  percent  after  20  minutes  and  14  percent  after  an  hour. 
From  this  it  may  be  inferred  that  seed-corn  is  uninjured  by  as  much 
as  10  minutes'  soaking  in  either  kind  of  alcohol,  but  that  more  than 
this  is  dangerous,  and  that  injury  will  begin  to  appear  after  20  or  30 
minutes'  treatment — sooner  if  the  solvent  is  wood  alcohol. 

Lysol. — This  highly  odoriferous  coal-tar  product  was  applied  to 
seed-corn  in  twenty-one  lots  of  50  kernels  each,  and  in  aqueous  solu- 
tions of  1  percent,  2  percent,  5  percent,  and  10  percent,  the  corn 
being  soaked  in  each  of  these  5  minutes,  10  minutes,  20  minutes,  and 
1  and  2  hours.  Another  lot  of  corn  was  soaked  for  5  minutes  in  pure 
lysol,  and  lysol  was  applied  to  seed-corn  at  the  rate  of  half  an  ounce 


12  BULLETIN  No.  130  [December, 

of  the  fluid  to  the  gallon  of  corn,  and  at  the  rate  of  an  ounce  to  the 
gallon.  No  injury  was  done  by  the  1  percent  solution  applied  in 
periods  up  to  two  hours,  and  the  2  percent  solution  was  harmless  up 
to  20  minutes.  Two  hours'  soaking  at  the  latter  strength  was  in- 
jurious, giving  a  germination  ratio  of  but  68  percent,  and  all  the 
plants  growing  were  more  or  less  injured.  The  5  percent  solution 
did  no  harm  when  used  for  5  or  10  minutes,  but  after  20  minutes' 
treatment  only  78  percent  of  the  kernels  grew,  while  after  2  hours' 
treatment  at  this  strength  all  the  corn  was  dead.  Even  5  minutes'  use 
of  a  10  percent  solution  proved  injurious.  Corn  treated  with  the 
pure  lysol  at  the  rate  of  half  an  ounce  to  a  gallon  of  the  corn  was 
uninjured,  92  out  of  100  kernels  of  it  germinating;  but  when  this 
strength  was  doubled,  the  germination  ratio  fell  to  73  percent.  From 
these  experiments  we  may  infer  that  a  2  percent  solution  of  lysol  in 
water  may  be  used  to  soak  the  seed  if  treatment  be  not  continued 
over  10  minutes,  and  that  half  an  ounce  of  the  undiluted  lysol  may 
be  stirred  into  a  gallon  of  corn  without  risk  of  injury. 

Kainit. — The  potash  fertilizer  known  as  kainit,  which  has  some- 
times been  recommended  as  a  repellent  to  the  corn  root-aphis,  was 
tested  on  300  kernels  divided  into  six  lots.  The  total  germination 
ratio  was  90  percent.  One  lot,  in  which  the  planted  seed  was  thickly 
covered  with  kainit,  fell  to  78  percent. 

Lime,  Sulphur,  and  Salt. — Saturated  solutions  of  either  lime  or 
salt  were  harmless  to  seed-corn  soaked  in  them  for  30  minutes  or 
less,  and  84  percent  of  the  kernels  germinated  when  planted  after 
rolling  iri  a  plaster  of  wet  salt,  none  of  the  plants  showing  injury. 
Simple  powdered  sulphur,  1  or  2  pounds  to  the  bushel  of  corn,  had 
no  effect  upon  the  seed,  however  it  was  applied ;  neither  did  mixtures 
of  lime,  sulphur,  and  salt,  or  lime,  sulphur,  and  blue  vitriol,  unless 
these  were  applied  for  more  than  an  hour.  After  2  hours'  soaking 
in  a  solution  of  lime  and  sulphur  (15  pounds  of  each  to  50  gallons 
of  water),  seed-corn  sprouted  in  a  ratio  of  80  percent,  with  an  ap- 
pearance of  injury  to  all  the  plants  which  grew.  A  ready-prepared 
solution  of  sulphur  sold  under  the  name  of  "Rex  Dip"  was  variously 
used  in  the  treatment  of  seed-corn,  and  in  every  case  without  notice- 
able effect  on  tTie  germination  of  the  seed  until  this  had  been  soaked 
in  it  for  more  than  an  hour.  Seven  hundred  kernels  divided  into  four- 
teen lots  of  50  each  and  soaked  for  periods  varying  from  5  minutes  to 
an  hour  gave  a  general  germination  average  of  96  percent,  4  percent 
more  than  the  normal  for  untreated  corn  of  this  sample.  Two  hun- 
dred kernels  planted  in  four  lots  of  50  each,  and  soaked  for  2  hours, 
gave  a  ratio  of  88  percent  of  kernels  germinating. 

Chlorid  of  Lime. — Used  in  a  saturated  solution,  or  applied  by 
rolling  the  kernels  in  a  wet  plaster,  chlorid  of  lime  was  without  effect 
on  the  sprouting  of  the  seed  or  the  growth  of  the  plants.  Two  hun- 
dred kernels  soaked  for  5  to  30  minutes  in  the  solution  grew  in  a 
ratio  of  98  percent,  and  100  kernels  rolled  in  a  thin  paste  of  the  wet 
lime  all  grew.  Dry  chlorid  mixed  with  the  seed  was  also  harmless 
to  50  kernels. 


1908]  REPELLENTS  AGAINST  CORN  ROOT-APHIS  13 

Carbon  Bisulphid. — A  carbon  bisulphid  treatment  was  also  harm- 
less so  far  as  tested  by  stirring  the  undiluted  fluid  into  the  corn  at 
the  rate  of  2  and  4  ounces  per  gallon,  or  by  soaking  the  seed  in  the 
fluid  for  10  minutes. 

Copper  Sulphate. — Seed-corn  soaked  in  a  saturated  solution  of  blue 
vitriol  was  uninjured  after  5  and  10  minutes'  treatment,  and  90  per- 
cent of  the  seed  germinated  after  20  minutes'  soaking,  but  only  83 
percent  after  30  minutes  (16  percent  of  the  plants  being  injured)  and 
80  percent  after  an  hour,  all  of  these  last  plants  showing  injury. 

Iron  Sulphate. — Two  hundred  kernels  of  seed-corn  soaked  in  a 
saturated  solution  of  copperas  for  periods  varying  from  5  minutes 
to  16  hours,  and  in  lots  of  50  kernels  each,  were  uninjured  as  to 
germination,  averaging  95  percent. 

Tobacco-water. — Strong  solutions  of  tobacco-water,  obtained  by 
boiling  the  stems,  did  no  injury  to  seed  or  plant,  even  when  the  corn 
was  soaked  from  1  to  24  hours.  Three  hundred  and  fifty  kernels  thus 
treated,  100  of  them  for  the  longer  period,  gave  an  average  germina- 
tion ratio  of  98  percent. 

Musk. — Commercial  Tonquin  musk,  mixed  with  wood  alcohol  at 
the  rate  of  -1  part  of  musk  to  10  of  the  solvent,  did  no  injury  to  the 
seed  when  3  ounces  of  the  mixture  were  thoroly  stirred  into  a  gallon 
of  corn.  Neither  a  5  percent  nor  a  10  percent  solution  of  the  musk 
in  ordinary  alcohol  injured  the  seed  after  5  minutes'  soaking,  but  a 
longer  exposure  diminished  the  ratio  of  germination,  and  soaking  for 
an  hour  was  decidedly  injurious.  These  effects  were,  however,  quite 
possibly  due  to  the  alcohol. 

Mustard. — Mustard  was  injurious  when  applied  in  the  powdered 
form,  but  16  hours'  soaking  in  a  saturated  solution  with  water  did 
not  affect  germination. 

Miscellaneous  substances. — The  proprietary  insecticides  "Scale- 
cide,"  "Con  Sol,"  "Calcothion,"  and  "Frutolin"  were  all'  without  effect 
upon  the  seed,  tested  by  soaking  the  seed  in  them  for  5  to  30  minutes. 
"Scalecide"  was  used  in  5  and  10  percent  mixtures  with  water,  "Con 
Sol"  in  a  2l/2  percent  mixture,  and  "Calcothion"  arid  "Frutolin"  pure. 
Twenty  lots,  amounting  to  1000  kernels,  were  soaked  in  these  various 
insecticides,  none  giving  less  than  a  germination  ratio  of  92  percent, 
and  most  of  them  rising  to  98  and  100  percent. 

Fifty  kernels  of  corn  left  in  coal-tar  for  a  minute  and  planted  at 
once,  all  grew  but  one — very  slowly,  however,  and  with  more  or  less 
appearance  of  injury,  the  plants  averaging  only  3j/3  inches  in  height 
four  weeks  after  planting.  Soaked  in  coal-tar  for  16  hours,  only  11 
kernels  grew  out  of  50,  and  the  plants  from  these  were  all  stunted  and 
otherwise  injured. 

Tar-water,  obtained  by  pouring  water  upon  coal-tar  and  stirring 
the  two  together  and  leaving  for  a  time  to  settle,  did  no  injury  to  50 
grains  of  seed  soaked  for  half  an  hour  or  an  hour. 

Camphor  was  imperfectly  tested  by  soaking  seed-corn  for  10  min- 
utes and  for  an  hour  in  a  saturated  solution  of  the  gum  in  alcohol. 


BULLETIN  No.  130 


[December, 


After  10  minutes'  soaking  all  the  seed  grew,  but  after  one  hour's 
treatment  all  but  2  kernels  out  of  50  were  killed.  A  light  application 
of  the  solution  at  the  rate  of  about  3  ounces  to  the  gallon  of  corn 
produced  no  effect,  49  kernels  out  of  50  growing,  and  the  plants  being 
uninjured  and  of  maximum  height  after  3  weeks. 

The  more  important  of  these  statistical  data  are  brought  together 
in  the  table  following. 

PRINCIPAL  POT  EXPERIMENTS  WITH  REPELLENTS,  1906 


No  Treatment  of  Seed.     Check  Pots 


No.  of  kernels 

Percent  to  grow 

No  treatment        ...        

1750 

96 

Treatment  of  Seed  with  Kerosene 


Quantity  or  time 

No.  of  kernels 

Percent  to  grow 

i  oz  —  2  oz    to  one  gallon                                  

800 

98 

2%  oz  —  3/^  oz   to  one  gallon  

200 

92 

10  minutes'  soaking  .... 

200 

88 

20        "             "         

200 

93 

4  hours'                      

50 

2 

16     "                "         

200 

82 

19    "                "           

100 

3 

Treatment  of  Seed  with  Crude  Petroleum 


Time  in  petroleum 

No.  of  kernels 

Percent  to  grow 

100 

91 

20  to  30     "            

100 

56 

1  to  3  hours  .  .          .             

150 

77 

19  to  74  "                       

250 

54 

Treatment  of  Seed  with  Oil  of  Lemon  and  Alcohol 


Quantity  or  time 

No.  of  kernels 

Percent  to  grow 

Oil  of  lemon,  10%  mixture: 
3  oz   to  gallon  of  corn  

100 

98 

20  to  60  minutes'  soaking    

150 

87 

19  hours'  soaking  

50 

58 

Oil  of  lemon,  33>i  %   mixture: 
5  to  10  minutes'  soaking                         

100 

99 

20  to  30          "            "        

100 

99 

1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS 

Treatment  of  Seed  with  Solutions  of  Carbolic  Acid 


15 


Strength 

Time 

No.  of  kernels 

Percent  to  grow 

200 

99 

5 

5  to  30       "        

200 

96 

10        " 

5  to  30        "              

200 

9 

30        " 

5  to  30       "       

200 

1 

Treatment  of  Seed  with  Formalin  Solutions 


Strength 

Time 

No.  of  kernels 

Percent  to  grow 

4  percent 
25"  ,  " 
.25 
50 

5  to  30  mini 
5  minutes  .  . 

ites  

200 
50 
150 
50 

94 

74 
34 
0 

10  to  30  mini 
30  minutes 

ites  

Treatment  of  Seed  with  Alcohol 


Time  in  alcohol 

No.  of  kernels 

Percent  to  grow 

Common  alcohol: 
5  to  20  minutes  

150 

98 

30  minutes  

50 

66 

Wood  alcohol: 
5  to  10  minutes  

100 

95 

20  minutes            

*           50 

74 

60        "       

50 

14 

: 

Treatment  of  Seed  with  Lysol  in  Water 


Strength 

Time  or  quantity 

No.  of  kernels 

Percent  to  grow 

1  perc 

2 
2 
5 
5 
5 
10 
10 
100 
100 
100 

ent 

5  to  120  minutes.        

200 
150 
50 
100 
50 
50 
100 
100 
50 
100 
100 

99 
95 
68 
96 

78 
0 
78 
0 
2 
73 
92 

5  to  20         "        

2  hours  

5  to  10  minutes  

2  hours  

5  to  10  minutes  

20  to  60        "        

5  minutes          

1  oz.  to  gal.  corn  

/4  oz.  to  gal.  corn  

A  CORN-FIELD  EXPERIMENT,  1906 

Precautions  preliminary  to  a  large  field  experiment  having  been 
thus  taken,  and  injury  to  the  seed  thus  guarded  against,  the  way  was 
open  to  a  practical  test  of  the  most  promising  of  these  repellents,  to  be 
made  by  planting  parts  of  the  same  field  with  corn  treated  with  each 
of  them,  leaving  other  parts  untreated  as  a  check. 


16  BULLETIN  No.  130  [December, 

THE   EXPERIMENTAL  FIELD 

For  this  purpose,  after  a  careful  examination  of  many  fields  in 
the  vicinity  of  Elliot,  Ford  county,  by  one  of  my  assistants,  Mr.  E.  O. 
G.  Kelly,  choice  was  made  of  twenty  acres  of  dark  rich  loam,  level 
and  of  a  uniform  quality,  on  the  farm  of  Mr.  James  Jones,  one  and 
a  half  mile  northeast  of  Elliot. 

This  ground  had  been  in  corn  the  preceding  year,  and  it  was 
heavily  infested  by  the  corn-field  ant.  The  old  stalks  were  harrowed 
down  and  burned  April  24  and  25,  and  the  field  was  plowed  to  a  depth 
of  4  to  6  inches  April  26  to  28,  with  a  gang  of  two  plows,  each  cutting 
a  furrow  15  inches  wide.  It  was  then  twice  harrowed  with  a  toothed 
harrow — the  last  time  May  7 — and  was  planted  May  8  to  11,  in  rows 
80  rods  long,  372  hills  to  the  row,  the  hills  2>l/2  feet  apart  each  way. 

INSECT   INFESTATION   OF   FIELD 

A  number  of  ants'  nests  in  this  field,  critically  examined  previous 
to  April  26,  all  contained  eggs  and  recently  hatched  young  of  the  corn 
root-aphis.  The  degree  of  infestation  of  the  field  was  ascertained  by 
counting  the  nests  of  the  corn-field  ant  overturned  by  the  plow. 
Eleven  hundred  and  forty-two  nests  were"  found  in  62  furrows  cross- 
ing the  field  and  aggregating  15^  miles  in  length.  This  was  at  the 
rate  of  74  ants'  nests  to  the  mile  of  furrow,  516  to  the  acre,  or  10,320 
to  the  entire  field. 

Nineteen  days  later  250  hills  of  the  corn  in  the  check  plots  of  this 
field  were  found  to  harbor  an  average  of  62  ants  to  the  hill, — equiva- 
lent to  nearly  five  millions  in  the  entire  field ;  and  within  six  weeks 
from  the  time  of  planting,  the  check  hills  averaged  162  root-lice, — 
equivalent  to  twelve  and  a  half  millions  of  those  insects  to  the  field. 

Even  this  statement  does  not  fully  describe  the  burden  of  infesta- 
tion with  which  our  experimental  field  began  the  year.  During  his 
tramp  of  15^  miles,  backward  and  forward  behind  the  plow,  Mr. 
Kelly  counted  also  6519  white-grubs  exposed  in  plowing,  which  is 
at  the  rate  of  nearly  3000  of  these  destructive  insects  to  the  acre,  or 
59,000  for  the  entire  field.  Of  course  only  a  small  part  of  the  grubs 
in  the  soil  were  brought  to  view  by  the  plowing,  and  this  number 
may  reasonably  be  trebled  or  quadrupled  for  an  estimate  of  the  whole 
number  present. 

DESCRIPTION  OF  THE  EXPERIMENT 

The  ground  being  thus  selected,  found  thus  infested,  and  made 
ready  for  planting,  an  experiment  was  started  May  9  with  four 
principal  substances — kerosene,  oil  of  lemon,  formalin,  and  carbolic 
acid — and  with  three  others,  to  which  less  importance  was  attached — 
flowers  of  sulphur,  chlorid  of  lime,  and  "Rex  Dip."  The  experiment 
was  laid  out  as  follows : 

The  first  50  rows  from  the  east  side  of  the  field  were  planted  with 
corn  not  treated,  and  available,  consequently,  as  a  check.  The  next 
24  rows  were  planted  with  seed  treated  with  a  3  percent  solution  of 


1908]  REPELLENTS  AGAINST  CORN  ROOT-APHIS  17 

crude  carbolic  acid  in  water.  Three  ounces  of  this  mixture  was 
poured  upon  a  gallon  of  corn,  which  was  thoroly  stirred  until  every 
kernel  was  moistened,  the  surplus  being  allowed  to  drain  away.  Not- 
withstanding its  slightly  moist  condition,  the  corn  ran  out  of  the 
planter  as  well  as  if  it  had  been  dry. 

The  20  rows  next  this  strip  were  planted  with  ordinary  seed  left 
as  a  check ;  and  ,for  the  next  12  rows  the  corn  was  treated  with  kero- 
sene, half  a  fluid  ounce  of  the  pure  oil  being  thoroly  mixed  with  a 
gallon  of  the  seed  just  before  it  was  put  into  the  box. 

The  next  12  rows  were  planted  with  corn  treated  with  oil  of 
lemon.  For  this  purpose  one  part,  by  measure,  of  the  oil  was  mixed 
with  nine  parts  of  ordinary  alcohol,  and  3  fluid  ounces  (6  tablespoon- 
fuls)  of  this  solution  was  thoroly  stirred  into  a  gallon  of  corn,  which 
was  then  drained  and  put  at  once  into  the  planter  box. 

The  next  8  rows  were  left  as  a  check ;  and  for  the  plot  of  12  rows 
adjoining,  the  seed  was  treated  with  formalin  reduced  to  a  3  percent 
solution  by  the  addition  of  water.  Three  ounces  of  this  mixture 
was  thoroly  stirred  with  a  stick  into  a  gallon  of  corn,  which  was  then 
carefully  drained  and  put  into  the  planter  at  once. 

On  the  llth  of  May,  in  another  part  of  the  field,  28  rows  of  corn 
were  planted,  the  seed  for  which  had  been  treated  with  a  solution  of 
lime  and  sulphur  known  as  "Rex  Dip,"  1  part  of  this  substance  to  10 
parts  of  water.  A  pint  of  the  mixture  was  poured  upon  a  gallon  of 
seed-corn,  which  was  then  thoroly  stirred,  and  after  20  minutes'  soak- 
ing the  seed  was  drained,  being  stirred  in  the  meantime  to  dry  it 
partially,  in  order  that  it  might  work  well  in  the  planter. 

Next  to  this  plot,  a  strip  of  8  rows  was  left  as  a  check,  and  the 
following  8  rows  were  planted  with  corn  treated  with  flowers  of  sul- 
phur. The  grain  was  dampened  slightly  to  make  the  sulphur  stick, 
and  a  quarter  of  a  pound  of  the  latter  was  stirred  thoroly  into  a  gal- 
lon of  corn,  completely  covering  all  the  kernels. 

Finally,  16  rows  adjacent  were  planted  with  seed  which  had  been 
soaked  for  10  minutes  in  half  a  pint  of  a  saturated  aqueous  solution 
of  chlorid  of  lime  to  the  gallon  of  corn. 

The  ground  was  reported  to  be  very  dry  at  the  time  of  planting, 
and  the  young  weeds  in  the  field  were  all  dead  as  a  consequence.  Its 
condition  was  evidently  not  unusual,  however,  since  a  heavy  rain  is 
recorded  for  May  2,  and  another  followed  May  8.*  Nevertheless 
there  was  some  deficiency  of  moisture,  for  the  soil  was  lumpy  after 
plowing,  and  the  sprouting  of  the  seed  was  said,  on  the  22d,  to  have 
been  delayed  somewhat  by  dry  weather. 

Fifty  hills  of  corn  were  examined  on  the  latter  date  in  one  of  the 
checks,  and  15  were  found  to  contain  root-lice  and  ants.  Odors  of 
carbolic  acid,  oil  of  lemon,  and  kerosene  were  still  perceptible  on  the 
kernels  a  week  after  planting,  but  the  corn  treated  with  formalin  had 
no  noticeable  smell. 


*  Rains  fell  at  this  place  as  follows:     April  8,  13,  24,  30   (shower);  May  1,  2  (heavy),  8, 
18   (slight),  26  (heavy),  277  and  30.     The  fields  and  roads  were  said  to  be  muddy  June  1. 


18  BULLETIN  No.  130  [December, 

RESULTS  OF  THE  EXPERIMENT.      FIRST  INSPECTION 

The  first  general  inspection  of  the  field  was  made  by  Mr.  Kelly 
May  28  to  30,  when  800  hills  were  dug  up  in  the  various  plots  and  the 
ants  and  root-lice  were  carefully  counted.*  Two  hundred  and  fifty  of 
these  hills  were  from  the  check  plots,  100  each  from  the  principal 
experimental  plots — those  with  carbolic  acid,  kerosene,  formalin,  and 
oil  of  lemon — and  fifty  each  from  the  three  remaining  plots  whose 
seed  had  been  treated  with  sulphur,  "Rex  Dip,"  and  chlorid  of  lime. 

Percentages  of  hills  infested  19  days  after  planting. — At  this  time, 
a  month  after  the  plowing  of  the  field  and  19  days  after  planting, 
57  percent  of  the  250  hills  dug  up  in  the  check  plots  were  infested 
by  ants.  The  corresponding  averages  for  each  of  the  four  principal 
experimental  plots  were  as  follows :  oil  of  lemon,  23  percent  infested ; 
kerosene,  31  percent ;  formalin,  33  percent ;  and  carbolic  acid,  49  per- 
cent. The  ratios  for  the  less  important  experiments,  from  each  jof 
which  50  hills  were  dug  up,  were  54  percent  for  the  sulphur  plot,  70 
percent  for  the  "Rex  Dip,"  and  48  percent  for  the  chlorid  of  lime. 
Otherwise  stated,  using  the  condition  of  the  check  plot  as  a  basis  of 
comparison,  the  plot  treated  with  the  oil  of  lemon  showed  an  improve- 
ment of  60  percent  in  number  of  hills  infested  by  ants;  the  kerosene 
plot,  a  46  percent  improvement ;  the  formalin  plot.  42  percent ;  and 
the  carbolic  acid  plot,  14  percent.  The  three  other  plots  showed  no 
improvement  except  possibly  the  chlorid  of  lime. 

Not  all  the  hills  containing  ants  at  this  time  contained  root-lice 
also,  but  there  were  no  root-lice  where  there  were  no  ants.  The  ratios 
of  infestation  of  corn  hills  by  the  root-aphis  for  the  five  plots  were 
as  follows :  checks,  53  percent ;  oil  of  lemon,  14  percent ;  kerosene, 
20  percent ;  formalin,  28  percent,  and  carbolic  acid,  39  percent.  The 
corresponding  ratios  of  improvement  in  respect  to  aphis  infestation 
were  these :  oil  of  lemon,  a  benefit  of  74  percent ;  kerosene,  62  per- 
cent ;  formalin,  47  percent ;  and  carbolic  acid,  26  percent. 

It  is  a  suggestive  fact  that  while  the  infested  hills  of  the  checks 
contained  an  average  of  21  ant  larvae  to  the  hill,  none  of  the  hills 
treated  with  the  three  most  odorous  substances,  oil  of  lemon,  kerosene, 
and  carbolic  acid,  contained  so  much  as  a  single  larval  ant.  In  the 
formalin  plot,  however,  there  were  about  as  many  larvae  to  the  in- 
fested hill  as  in  the  checks.  As  the  ants  take  assiduous  and  anxious 
care  of  their  young,  the  absence  of  larvae  from  the  treated  hills,  even 
where  the  workers  themselves  were  numerous,  is  evidence  that  con- 
ditions there  were  offensive  to  the  ants. 

In  view  of  the  observed  effect  of  an  overdose  of  kerosene  on  the 
young  plant,  as  described  in  the  earlier  part  of  this  article,  it  is  im- 
portant to  note  that  no  dwarfing  or  distortion  of  the  corn  plants  was 
seen  in  any  of  these  experiments. 

Average  numbers  of  insects  19  days  after  planting. — Turning  now 
to  the  number  of  both  kinds  of  insects  in  these  plots,  irrespective  of 

*The  owner  of  this  field  was  paid  at  an  agreed  rate  for  all  hills  dug  up  or  injured  in 
the  course  of  our  experiments. 


1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  19 

the  number  of  hills  of  corn  infested  by  them,  we  find  an  average  of 
66  ants  and  23  root-lice  to  the  hill  in  the  checks,  9  ants  and  2  root- 
lice  to  a  hill  in  the  oil  of  lemon  plot,  16  ants  and  3  root-lice  in  the 
kerosene  plot,  30  ants  and  6  root-lice  in  the  formalin  plot,  and  25  ants 
and  12  root-lice  to  the  hill  in  the  plot  treated  with  carbolic  acid.  The 
ratios  of  benefit  in  respect  to  the  numbers  of  root-lite  were  conse- 
quently as  follows.  With  respect  to  ants :  oil  of  lemon,  86  percent 
benefit ;  kerosene,  76  percent ;  formalin,  55  percent ;  and  carbolic  acid, 
62  percent.  With  respect  to  root-lice :  oil  of  lemon,  83  percent  benefit ; 
kerosene,  87  percent ;  formalin,  74  percent ;  and  carbolic  acid,  52  per- 
cent. The  use  of  the  three  secondary  applications,  on  the  other  hand, 
"Rex  Dip,"  chlorid  of  lime,  and  sulphur,  had  evidently  accomplished 
comparatively  little.  In  the  plot  treated  with  chlorid  of  lime  there 
were  31  ants  and  25  aphids  to  the  hill;  in  that  treated  with  sulphur, 
45  ants  and  31  aphids;  and  in  the  plot  treated  with  "Rex  Dip,"  72 
ants  and  53  aphids — the  last  two  of  these  numbers  being  actually 
greater  than  those  for  the  checks. 

The  total  normal  infestation  of  this  field  at  this  time,  as  shown  by 
the  condition  of  the  checks,  was  240,000  ants  and  124,000  root-lice  to 
the  acre.  The  aphids  were  all  in  hills  of  corn,  while  only  so  many 
of  the  ants  were  there  established  as  was  necessary  to  the  purposes 
of  the  colony,  the  central  home  of  which  was  commonly  outside  the 
hill  between  the  rows  of  corn.  The  data  of  the  foregoing  discussion 
are  briefly  presented  in  the  tables  on  page  20. 

RESULTS  OF  THE  EXPERIMENT.       SECOND  INSPECTION 

June  21,  43  days  after  planting,  a  second  count  was  made  of  both 
ants  and  aphids  in  250  hills — 50  hills  each  for  the  check  and  for  the 
four  principal  experimental  plots.  At  this  second. counting,  73  percent 
of  the  hills  in  the  check  were  infested  with  ants,  22  percent  of  those 
in  the  oil  of  lemon  plot,  44  percent  in  the  kerosene  plot,  46  percent 
in  the  formalin  plot,  and  76  percent  in  the  plot  treated  with  carbolic 
acid.  A  few  hills  contained  ants  which  did  not  contain  root-lice  also. 
The  corresponding  ratios  of  infestation  by  root-aphids  for  these  five 
plots  were  as  follows:  check,  73  percent;  oil  of  lemon,  20  percent; 
kerosene,  40  percent;  formalin,  46  percent;  carbolic  acid,  74  percent. 
In  respect  to  number  of  insects  in  each  lot  of  50  hills  dug  from  the 
various  plots,  we  find  the  difference  quite  as  marked.  The  check  plot 
contained  39  ants  and  166  aphids  to  the  hill ;  the  oil  of  lemon  plot,  8 
ants  and  18  aphids ;  the  kerosene  plot,  16  ants  and  52  aphid's ;  the 
formalin  plot,  20  ants  and  64  aphids ;  and  the  carbolic  acid,  32  ants 
and  139  aphids. 

Converting  these  data  into  percentages  of  improvement,  by  com- 
paring the  ratios  for  each  experiment  with  those  of  the  check,  we 
find  that  the  benefit  to  the  plot  treated  with  oil  of  lemon  was  70  per- 
cent in  number  of  hills  infested  by  ants,  73  percent  in  hills  infested 
by  aphids,  79  percent  in  the  number  of  ants  in  the  plot,  and  89  percent 
in  the  number  of  aphids.  The  corresponding  ratios  of  benefit  for  the 


20 


BULLETIN  No.  130 


[December, 


kerosene  plot  are  40  percent  in  hills  infested  by  ants,  45  percent  ir>  V^ 
those  infested  by  aphids,  59  percent  in  number  of  ants,  and  69  percent 
in  number  of  aphids.  In  the  formalin  plot  the  benefit  for  hills  infested 
by  ants  and  by  aphids  was  37  percent  for  each,  and  the  benefit  in 
number  of  ants  in  the  plot  was  49  percent,  and  in  number  of  aphids, 
61  percent.  In  the  carbolic  acid  plot,  on  the  other  hand,  the  numbers 
of  hills  infested  by  ants  and  by  aphids  were  somewhat  larger  than 
in  the  check. 

INSPECTIONS  OF  MAY  AND  JUNE,  1906 
Percent  of  Hills  infested 


Check 

Oil  of 
lemon 

Kerosene 

Carbolic 
acid 

Formalin 

By  ants: 

After  19  days 

57 

23 

31 

49 

33 

After  43     " 

73 

22 

44 

76 

46 

By  aphids: 

After  19  days 

53 

14 

20 

39 

28 

After  43     " 

.73 

20 

40 

74 

46 

Insects  to  the  Hill 


Check 

Oil  of 
lemon 

Kerosene 

Carbolic 
acid 

Formalin 

Ants: 

After  19  days 

66 

9 

16 

25 

30 

After  43     " 

39 

8 

16 

32 

20 

Aphids: 

After  19  days 

23 

2 

3 

12 

6 

After  43     ' 

166 

18 

52 

139 

64 

Percentages  of  Benefit  from  various  Treatments 


Oil  of  lemon 
Kerosene 
Carbolic  acid 
Formalin 

Benefit  in  hills  infested 

Benefit  in  No.  of  insects 

After  19  days 

After  43  days 

After  19  days 

After  43  days 

By 
ants 

By 
aphids 

By 
ants 

By 
aphids 

Ants 

Aphids 

Ants 

Aphids 

60 
46 
14 

42 

74 
62 
26 

47 

70 
40 
00 
37 

73 
45 
00 

37 

86 
76 
62 

55 

83 
87 
52 
74 

79 
59 
18 
49 

80 
69 
15 
61 

Library,  New  Mexico  State  College 

1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  21 

*  FIRST  AND  SECOND  INSPECTIONS  COMPARED 

Comparing  next  the  conditions  found  May  28  and  June  21,  we  find 
that  the  number  of  hills  infested  in  the  check  had  increased  between 
these  dates  from  57  percent  to  73  percent  for  ants,  and  from  53  per- 
cent to  73  percent  for  the  aphids ;  while  the  number  of  ants  to  the 
hill  had  diminished  from  66  to  39  and  the  number  of  aphids  to  the 
hill  had  increased  from  23  to  166.  The  number  of  the  aphids,  it  will 
be  seen,  had  increased  sevenfold. 

Rate  of  increase  of  root-lice  in  the  field. — The  period  of  active 
multiplication  of  the  root-aphis  in  the  field  commonly  continues  until 
early  October,  approximately  six  times  the  period  within  which  we 
found  a  sevenfold  increase.  If  this  rate  of  increase  were  maintained 
until  the  end  of  the  season,  the  124,000  aphids  per  acre  found  May  28 
would  multiply  by  October  1  to  more  than  14,340,000,000,  or  39,000  to 
the  hill  of  corn.  This  computation  of  the  actual  rate  of  multiplication 
of  the  corn  root-aphis  in  the  field  is  sufficient  to  account  completely  for 
any  amount  of  injury  which  these  insects  may  do  to  the  crop  under 
conditions  favorable  to  their  increase. 

RESULTS  OF  THE  EXPERIMENT.      THIRD  INSPECTION 

On  the  17th  of  July  Mr.  Kelly  reported  a  conspicuous  difference 
in  height  between  the  corn  on  the  experimental  strips  and  that  on  the 
checks — a  difference  so  great,  indeed,  that,  as  one  looked  across  the 
field,  it  seemed  to  lie  in  alternate  ridges  and  hollows,  the  ridges  corre- 
sponding to  the  experimental  strips  and  the  hollows  to  the  checks.  The 
ground  being  perfectly  level,  these  differences  were  evidently  due  to 
the  more  rapid  growth  of  the  corn  in  the  experimental  plots ;  or,  more 
correctly  speaking,  to  an  arrest  of  growth  in  the  checks  resulting  from 
the  greater  drain  of  insect  injury  where  the  corn  had  not  been  pro- 
tected by  a  previous  treatment  of  the  seed.  Visiting  this  field  July  21, 
I  noticed  that  the  central  rows  of  the  check  strips  were  shortest,  and 
the  central  rows  of  the  experimental  strips  were  tallest,  the  transition 
from  one  to  the  other  being  gradual.  On  passing  down  a  central 
check  row,  the  highest  stalks  reached,  on  the  average,  to  my  elbows ; 
and  on  walking  down  the  central  row  of  an  experimental  strip,  the 
tallest  stalks  were  found  to  reach  nearly  to  the  top  of  my  head. 

To  verify  this  observation,  measurements  were  made  of  the  tallest 
stalks  in  214  hills  of  one  of  the  checks,  and  in  157  hills  of  the  carbolic 
acid  plot.  The  first  of  these  averaged  36  inches  and  the  second  62 
inches.  The  height  of  the  corn  in  the  check  strip  was  less  by  42  per- 
cent than  that  in  the  experimental  plot,  and  this  was  the  measure  of 
an  injury  by  insects  in  the  former  which  had  been  prevented  in  the 
latter  by  the  treatment  of  the  seed  This  striking  difference  was  quite 
as  obvious  to  the  eye  August  27,  after  all  the  corn  had  tasseled. 

RESULTS  OF  THE  EXPERIMENT.      FOURTH  INSPECTION 

What  proved  to  be  a  final  inspection  of  this  field  was  made  Sep- 
tember 20,  when  the  hills  and  both  fertile  and  barren  stalks  were 


22  BULLETIN  No.  130  [December, 

counted  in  six  rows  of  the  checks  and  in  three  rows  each  of  the  four 
experimental  plots. 

Number  of  hills  of  corn  to  the  row. — The  following  were  the  aver- 
age number  of  hills  of  corn  to  the  row  372  hills  long.  In  the  check, 
329^  hills;  in  the  carbolic  acid  plot,  328;  oil  of  lemon,  326;  formalin, 
317;  kerosene,  282.  In  other  words,  11.4  percent  of  the  places  for 
hills  were  without  corn  in  the  check,  11.8  percent  in  the  carbolic  acid 
plot,  12.4  in  the  oil  of  lemon  plot,  14.7  percent  in  the  formalin  plot, 
and  24.2  percent  in  the  plot  treated  with  kerosene.  The  differences 
between  the  check  on  the  one  hand  and  the  plots  treated  with  carbolic 
acid  and  oil  of  lemon  on  the  other  are  doubtless  insignificant,  and  per- 
haps the  formalin  plot  should  be  included  in  this  statement.  Consid- 
erable importance  must  be  attached,  however,  to  the  fact  that  more 
than  twice  as  many  hills  were  missing  in  the  plot  treated  with  kero- 
sene as  in  the  check,  three  rows  of  the  kerosene  plot  containing  271 
missing  hills  as  against  255  missing  from  six  rows  of  the  check.  In 
view  of  the  injurious  effect  of  kerosene  upon  the  seed,  as  shown  by 
our  insectary  work  and  by  our  field  experiment  of  1905,  we  can  only 
suppose  that  some  injury  was  done  even  by  the  r*inimum  amount  of 
kerosene  used  in  this  experiment  of  1906. 

Number  of  stalks  of  corn  to  the  row. — The  number 'of  stalks  to 
the  row  in  these  various  plots  was  as  follows :  check,  621 ;  oil  of 
lemon,  641;  formalin,  545;  carbolic  acid,  543;  kerosene,  511.  The 
plot  treated  with  the  oil  of  lemon,  it  will  be  noticed,  contained  20 
stalks  more  to  the  row  than  the  check — an  increase  of  3.2  percent, 
apparently  due  to  a  complete  destruction  of  the  plants  by  the  insects 
in  the  check,  against  which  the  experimental  strip  had  been  protected 
by  its  treatment.  In  the  remaining  plots,  on  the  other  hand,  the  num- 
ber of  stalks  was  diminished  in  the  experimental  plots  from  12.2  per- 
cent in  the  formalin  strip  to  17.5  percent  in  the  kerosene — a  diminution 
which  can  only  be  accounted  for  on  the  supposition  that  a  certain 
amount  of  the  seed  was  injured  by  these  substances.  Indeed,  taking 
as  a  basis  of  comparison  the  number  of  stalks  in  the  plot  planted 
with  seed  which  had  been  treated  with  oil  of  lemon,  we  find  the  loss 
of  plants  in  the  kerosene  strip  to  have  been  20  percent  and  that  in 
the  other  plots  to  have  been  approximately  15  percent — all  due,  so  far 
as  one  can  see,  to  injury  to  the  seed  by  the  substances  employed. 

Ear-bearing  stalks  to  the  row. — The  most  significant  comparison 
of  these  plots  was  made  by  a  count  of  the  stalks  bearing  ears,  the 
number  of  barren  stalks  varying  greatly  according  to  the  treatment 
applied.  In  the  check  plot  were  412  ear-bearing  stalks  to  the  row; 
in  the  oil  of  lemon  plot,  526 ;  in  the  carbolic  acid  plot,  505 ;  in  the 
formalin  plot,  485 ;  and  in  the  kerosene  plot,  439, — all  four  numbers 
considerably  larger  than  those  of  the  check.  The  greatest  improve- 
ment to  be  seen  in  this  final  test  of  treatment  is  in  the  oil  of  lemon 
plot,  where  the  yield  in  ear-bearing  stalks  was  27.7  percent  greater 
than  that  of  the  check,  the  corresponding  ratios  of  increase  for  the 
remaining  plots  being  as  follows:  carbolic  acid,  22.6;  formalin,  17.7; 


1908] 


REPELLENTS  AGAINST  CORN  ROOT -APHIS 


23 


kerosene,  6.6.  It  will  be  noticed  that  notwithstanding  the  fact  that 
the  kerosene  plot  contained  an  average  of  110  stalks  per  row  fewer 
than  the  check,  the  number  of  ear-bearing  stalks  was  27  per  row 
greater  than  in  the  check.  Even  the  kerosene,  tho  it  seemed  to  have 
lessened  the  stand  by  an  injury  to  the  seed,  had  increased  the  yield 
nearly  7  percent  by  protecting  the  corn  against  the  drain  of  root-louse 
attack,  thus  preventing  the  blighting  of  a  considerable  percentage  of 
the  remaining  stalks.  Under  the  conditions  present  during  this  season 
and  in  th:s  field1,  all  these  treatments  had  an  ultimate  beneficial  result, 
according  to  the  data  thus  repeatedly  and  carefully  collected,  the 
actual  ratio  of  benefit  being,  however,  nearly  four  times  as  great  from 
the  use  of  the  oil  of  lemon  as  from  the  use  of  kerosene. 

INSPECTION  OF  SEPTEMBER  20 


Check 

Oil  of 
lemon 

Carbolic 
acid 

Formalin 

Kerosene 

Hills  to  the  row  

329.5 

326 

328 

317 

282 

Stalks  to  the  row.  .  .  . 

621 

641 

543 

545 

511 

Fertile  stalks  to  the  row 

412 

526 

505 

485 

439 

Thru  an  unfortunate  failure  of  the  tenant  farmer  controlling  this 
field,  I  was  disappointed  in  my  original  plan  to  harvest  the  plots  sepa- 
rately, measuring  and  weighing  the  product  of  each  in  comparison, 
and  the  difference  in  yield,  apart  from  these  differences  in  number,  can 
only  be  inferred  from  Mr.  Kelly's  note  of  September  20,  which  reads : 
"The  ears  and  the  stalks  in  the  checks  were  very  small,  much  smaller 
than  on  any  of  the  treated  plots.  The  ears  and  stalks  in  plots  treated 
with  oil  of  lemon  and  carbolic  acid  were  much  larger  than  those  in 
the  other  treated  plots,  and  much  larger  than  in  the  checks." 

GENERAL   FINAL  RESULT 

As  a  final  statement  of  the  most  important  result  of  the  various 
treatments  of  seed-corn  here  described,  it  may  be  said  that,  according 
to  the  data  of  this  experiment,  the  oil  of  lemon  treatment  increased 
the  yield  1159  ear-bearing  stalks  to  the  acre;  the  carbolic  acid  treat- 
ment, 945  such  stalks ;  the  formalin  treatment,  742 ;  and  the  kerosene 
treatment,  274. 

The  expense  of  all  the  treatments  was  trifling,  that  of  the  most 
costly — the  oil  of  lemon — amounting  to  about  ten  cents  an  acre  for 
material  used. 

COMPARISON  OF  INFESTED  FIELDS 

That  the  infestation  of  this  field  altho  heavy  enough  to  reduce 
the  yield  by  at  least  one  third,  was  not  by  any  means  extreme  is  shown 
by-  conditions  reported  by  Mr.  Kelly  from  a  field  of  20  acres  on  another 
farm  near  Elliot,  as  shown  by  an  inspection  made  September  14.  This 
latter  field  was  so  heavily  infested  by  the  corn  root-aphis  that  the 


24  BULLETIN  No.  130  [December, 

crop  was  virtually  destroyed.  In  a  plot  of  2000  hills  were  2467  stalks, 
of  which  95  percent  were  less  than  4  feet  high,  and  75  percent  were 
20  inches  high  or  less.  In  this  entire  plot  were  only  95  ears — a  num- 
ber equivalent  to  169  ears  to  the  acre — and  these  were  mainly  nubbins. 
Eleven  hundred  and  thirty-eight  h:lls  contained  still  living  plants,  and 
in  1093  of  them  the  root-aphis  was  still  present.  Four  hundred  and 
sixteen  hills  which  were  either  dead  or  withered,  dry,  and  barely 
living,  all  contained  the  root-aphis  at  the  time,  or  showed  by  the  bur- 
rows of  ants  along  the  roots  that  they  had  been  previously  infested. 
In  a  ne:ghboring  field  practically  uninfested,  with  which  this  is  to  be 
compared,  2000  hills  contained  4324  well-grown  stalks  with  4024  ears, 
only  201  of  which  were  nubbins. 

MORE  EXPERIMENTS  NECESSARY 

Our  field  experiment  of  1906,  decisive  as  it  seems,  is,  of  course, 
to  be  taken  as  applying  exactly  only  to  similar,  if  not  identical,  con- 
ditions— a  similar  soil  similarly  prepared,  equally  infested  with  the 
corn  root-aphis,  and  subject  to  similar  weather  conditions — and  with 
a  treatment  of  seed  identical  with  ours  in  all  particulars,  including 
materials  of  the  same  quality  and  strength.  How  far  the  results 
here  described  may  be  expected  to  apply  to  a  different  soil,  less 
heavily,  or  even  much  more  heavily,  infested,  more  thoroly  prepared, 
and  planted  during  either  a  very  wet  spring  or  a  very  dry  one,  with 
a  less  perfect  seed,  treated  with  slightly  different  chemicals  and  com- 
pounds, can  be  learned  only  by  repeated  and  varied  experiment.  In- 
deed, the  poss:bilities  of  useful  experiment  with  this  method  are  almost 
innumerable,  and  can  scarcely  be  exhausted  by  any  one  office,  however 
well  manned  and  equipped,  and  however  long  its  program  of  opera- 
tions. The  procedure  is  so  simple  and  so  inexpensive,  however,  that 
any  careful  corn  grower  can  test  it,  and  its  usefulness  in  ordinary 
practice  must  be  finally  determined  by  such  general,  careful,  and  oft- 
repeated  trial  as  farmers  themselves  may  think  it  worth  while  to 
make.  It  is  my  purpose  to  test  it  by  similar  operations  in  several 
successive  years,  the  results  of  which  will  be  reported  in  later  articles 
of  this  series,  and  it  w:'ll  greatly  help  us  to  an  early  practical  conclu- 
sion if  others  interested  will  experiment  carefully,  and  report  upon 
their  method's,  materials,  and  results. 

AN  ADDITIONAL,  MINOR  TEST 

Further  special  tests  on  the  reactions  of  ants  to  the  various  re- 
pellents of  our  list  were  made  by  planting,  close  around  burrows  of 
these  ants  in  the  field1,  a  few  hills  of  corn,  one  of  wh:ch  was  left  un- 
treated as  a  check,  the  remainder  being  treated  with  one  of  the  repel- 
lents as  a  test.  "Rex  Dip,"  formalin,  carbolic  acid,  oil  of  lemon,  kero- 
sene, chlorid  of  lime,  sulphur,  and  common  lime  were  tested  in  this 
vyay.  The  hills  so  planted  were  thus  immediately  exposed  to  infesta- 
tion, and  any  failure  of  the  ants  to  occupy  them  would  be  particularly 
significant.  The  test  plantings  were  all  made  by  Mr.  Kelly  April  $. 


1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  25 

in  a  field  near  Elliot,  and  the  results  were  ascertained  April  22,  when 
the  corn  was  from  3  to  5  inches  high.  All  the  test  hills  surrounding 
the  ants'  nests,  including  both  check  and  experimental  plantings,  were 
thoroly  infested  by  ants  arid  root-lice  where  the  seed  had  been  pre- 
viously treated  by  rolling  it  in  lime  or  sulphur,  by  soaking  for  10 
minutes  in  a  saturated  solution  of  chlorid  of  lime,  and  by  soaking  for 
10  minutes  in  a  10  percent  mixture  of  the  "Rex  Dip."  In  the  lime 
experiment,  5  hills  were-  planted  immediately  surrounding  an  ant's 
nest,  one  of  these  being  reserved  as  a  check;  in  the  sulphur  experi- 
ment, 4  hills  were  so  planted ;  and  in  that  with  chlorid  of  lime,  4  hills. 
In  that  with  "Rex  Dip,"  7  hills  were  planted  around  2  separate  nests 
of  the  ant.  The  results  of  these  experiments  thus  agree  with  those  of 
our  more  general  test  of  plot  plantings  in  the  field. 

As  a  test  of  the  formalin  treatment  of  the  seed,  2  ants'  nests  were 
surrounded  by  7  hills  of  corn,  3  around  one  and  4  around  the  other. 
In  each  case  one  of  the  hills  was  planted  with  untreated  seed,  and  the 
seed  for  the  others  was  soaked  in  a  4  percent  solution  of  formalin, — 
for  those  around  one  nest  for  5  minutes,  and  for  those  around  the 
other  for  10  minutes.  After  17  days,  both  check  and  experimental 
hills  were  all  completely  and  uniformly  infested  by  the  ants. 

In  an  experiment  with  the  oil  of  lemon,  4  hills  were  planted  around 
another  ant  nest,  three  of  them  with  treated  grains  and  one  as  a 
check.  Here  also  all  the  hills  were  infested  May  22. 

In  a  corresponding  experiment  with  kerosene,  10  hills  were  planted 
so  as  immediately  to  surround  2  nests  of  the  ants,  two  of  these  hills 
being  reserved  as  checks  and  the  other  eight  planted  with  corn  which 
had  been  moistened  with  kerosene  by  putting  a  single  drop  to  a  dozen 
grains  and  rolling  these  together  until  all  were  oily.  By  the  22d  of 
May  one  of  these  nests  was  completely  abandoned  by  the  ants,  which 
had  apparently  formed  another  nest  about  three  feet  away.  There 
were  no  aphids  on  roots  of  either  check  or  experimental  hills.  The 
other  nest  was  still  occupied,  and  there  were  a  few  aphids  on  the 
roots  of  the  check,  but  none  of  either  ants  or  aphids  on  the  experi- 
mental hills. 

Finally,  two  nests  were  surrounded  by  8  hills,  6  of  which  had  been 
treated  with  a  3  percent  solution  of  carbolic  acid — in  the  one  case 
soaking  for  5  minutes  and  in  the  other  for  10.  In  the  former  case 
the  roots  of  the  check  hill  were  covered  with  root-lice  attended  by  a 
few  ants,  while  those  of  the  three  experimental  hills  had  neither  ants 
nor  aphids  on  them.  In  the  latter  case  the  ants  had  abandoned  their 
nest,  and  neither  checks  nor  experimental  hills  were  infested. 

These  results  differ,  it  will  be  seen,  from  those  of  the  plot  plant- 
ings in  the  fact  that,  while  carbolic  acid  and  kerosene  apparently 
kept  the  insects  out  of  the  treated  hills  for  three  weeks,  oil  of  lemon 
and  formalin,  as  well  as  a  number  of  other  substances  tested,  were 
without  effect. 


26  BULLETIN  No.  130  [December, 

GENERAL  PROGRAM  OF  PREVENTION 

In  the  light  of  what  we  now  know  concerning  the  corn  root-aphis, 
the  following  measures  of  precaution  are  to  be  recommended  as  a 
practical  program. 

1.  A  short  rotation  period  in  corn,  especially  during  relatively  dry 
years.    A  single  year  in  corn  is  better  than  two  years,  and  a  period 
of  two  years  is  better  than  one  of  three.     Especially  if  the  crop  was 
visibly  injured  by  the  root-aphis  the  preceding  year,  or  if  more  than 
twenty  ants'  nests  to  the  mile  are  turned  up  by  the  plow,  it  is  best 
that  the  field  should  be  put  into  some  other  crop  than  corn — which 
other  is  a  matter  of  indifference,  since  no  other  is  liable  to  injury  by 
the  corn  root-aphis. 

It  must  be  remembered,  however,  that  even  a  field  in  corn  for 
the  first  time  may  become  infested  during  the  season  by  means  of 
winged  root-lice  coming  into  it  from  other  fields  in  its  neighborhood, 
this  infestation  perhaps  beginning  as  soon  as  the  corn  is  up ;  and  that 
the  rate  of  multiplication  of  these  insects  is  so  enormously  rapid,  under 
favorable  conditions,  that  such  a  new  infestation  sometimes  reaches 
destructive  numbers  before  the  first  season  is  over.  Even  the  shortest 
rotation  is  consequently  not  a  complete  preventive  where  the  root- 
aphis  has  become  so  generally  prevalent  as  it  now  is  in  most  parts  of 
the  Illinois  corn  belt.  This  is,  however,  the  most  reliable  of  all  known 
measures  of  prevention,  and  has  the  very  great  additional  advantage 
that  it  affords  complete  protection  against  another  of  the  great  insect 
pests  of  the  corn  field,  the  notorious  northern  corn  root-worm  (Dia- 
brotica  longicornis. 

2.  A  deep,  thoro,  and  repeated  stirring  of  old  corn  ground  in  fall 
or  spring  (or,  better  still,  in  winter,  where  possible)  as  a  preparation 
for  corn-planting.   So  quick  a  rotation  as  that  advised  in  the  preceding 
paragraph  is  perhaps  not  always  practicable,  and  is  at  any  rate  often 
unwelcome  and  will  not  always  be  practiced.    If  corn  is  to  be  planted 
on  ground  more  or  less  infested  by  the  root-aphis  the  preceding  year, 
injury  by  this  insect  may  be  greatly  diminished  by  such  a  preparation 
of  the  soil  as  will  repeatedly  break  up  the  underground  nests  of  the 
ants  and  scatter  the  contents  of  these  nests,  consisting  of  the  eggs  and 
young  of  the  ants  together  with  the  root-lice  and  their  eggs,  thoroly 
and  repeatedly  thru  the  dirt.    The  burrows  of  these  ants  do  not  often 
reach  to  a  depth  of  more  than  six  inches,  and  if  plowing  to  this  depth 
is  followed  by  a  deep  stirring  of  the  ground  with  a  disk  harrow,  or 
better,  with  a  corn  cultivator  set  into  the  ground  as  far  as  possible, 
the  attempts  of  the  ants  to  recover  their  propery  and  to  reconstruct 
their  nests  are  greatly  disturbed  and  rendered  largely  fruitless.     The 
more  thoroly,  frequently,  and  deeply  the  ground  is  stirred  in  the  in- 
terval between  the  first  plowing  and  the  corn-planting,  the  fewer  will 
be  the  root-lice  in  the  field  in  the  beginning  of  the  season.     By  this 
means  a  check  will  also  be  placed  upon  the  increase  of  the  ants  them- 

elves,  by  the  destruction  of  their  helpless  maggotlike  young  which 
they  have  brought  thru  the  winter  in  their  nests.      Furthermore,  the 


1908]  REPELLENTS  AGAINST  CORN  ROOT -APHIS  27 

young  weeds  in  the  field  on  which  the  root-lice  are  dependent  for  food 
until  the  corn  begins  to  grow  may  thus  be  so  thoroly  destroyed  as  to 
result  in  the  starvation  of  the  insects.  Fortunately  the  labor  of  this 
treatment  of  the  field  will  usually  be  more  than  repaid  by  an  improve- 
ment of  the  corn  crop  independent  of  all  protection  against  aphis  in- 
jury, this  being  practically  the  preparation  for  corn  especially  recom- 
mended by  our  best  teachers  of  high-grade  agriculture  and  practiced 
by  some  of  our  most  successful  corn  farmers. 

It  should  be  clearly  understood,  however,  that  this  measure  will 
not  destroy  all  the  root-aphids  in  the  field.  In  a  few  cases  ants'  nests 
will  go  so  deep  that  a  part  of  their  contents  will  be  undisturbed  by  the 
plow,  and  will  thus  remain  as  centers  of  infestation  from  which  the 
ants  and  aphids  spread  later  to  reoccupy  the  field.  Furthermore,  the 
corn-field  ant,  even  under  these  difficult  and  discouraging  conditions, 
will  sometimes  search  out  and  bring  together  again  at  least  a  part  of 
the  scattered  contents  of  its  burrows. 

The  outcome  of  several  carefully  conducted  experiments  with  this 
cultivation  method  of  preventing  the  root-louse  injury,  is  given  in 
Bulletin  104  of  the  Illinois  Agricultural  Experiment  Station,  pp.  102- 
123,  and  also  in  the  Twenty-fourth  Report  of  the  Illinois  State  En- 
tomologist, pp.  8-29. 

3.  The  maintenance  and  increase  of  the  fertility  of  the  soil.     The 
richer  the  ground  and  the  more  thrifty  the  crop  the  less,  other  things 
being  equal,  will  be  the  injury  to  plants  by  the  root-louse.     We  have 
no  present  evidence  that  these  insects  thrive  any  the  less  or  multiply 
any  less  rapidly  on  the  thrifty  corn  plant  than  on  one  poorly  nour- 
ished, but  there  is,  of  course,  no  doubt  that  the  plant  itself  suffers 
most  under  insect  attack  when  it  has  least  surplus  of  vigor  and  sap 
to  spare.     In  this  respect  also,  the  corn  root-aphis  helps  to  enforce 
the  teachings  of  a  better  agriculture,  increasing  the  penalty  of  a  poor 
management  by  still  further,  diminishing  the  yield  of  a  deteriorating 
soil. 

4.  Finally,  the  use  of  repellents  on  the  seed  as  described  in  this 
paper.     This  is  still  an  experimental  measure,  and  evidently  can  not 
be  commonly  relied  upon  until  we  know  more  of  its  general   and 
average  results.     It  seems  to  me  desirable,  however,  that  a  consider- 
able plot  should  be  planted  each  favorable  year  in  each  suitable  field, 
with  seed  treated  by  one  or  the  other  of  the  odoriferous  repellents  here 
discussed,  or,  still  better,  perhaps,  by  one  of  the  strongest-smelling 
fertilizers,  to  be  applied  by  means  of  a  fertilizer  dropper ;  and  that  the 
consequences  of  this  treatment  should  be  carefully  studied  by  a  com- 
parison of  the  product  of  this  plot  with  that  of  adjacent  parts  of  the 
field.     By  a  favorable  year  is  meant  one  in  which  the  spring  is  of  a 
fairly  average  character — a  little  drier  than  normal,  perhaps — and  in 
which,  consequently,  the  seed  is  likely  to  grow  quickly  and  the  plant  to 
get  a  good  and  early  start.     By  a  suitable  field  is  meant  one  in  corn 
for  a  year  or  more  preceding,  and  in  which  nests  of  the  corn-field  ant 
are  turned  out  in  plowing  at  the  rate  of  some  fifty  or  sixty  to  the  mile 


28  BULLETIN  No.  130  [December. 

of  furrow.  If  they  are  fewer  than  this  it  may  be  that,  in  a  year  favor- 
able for  corn,  no  sufficient  injury  to  any  of  the  plants  will  be  done  by 
the  root-lice  to  make  any  noticeable  difference  between  corn  growing 
from  treated  and  from  untreated  seed. 

As  a  safeguard  against  possible  injury  to  the  kind  of  seed  one 
is  using  by  the  kind  of  materials  one  may  chance  to  purchase,  and  in 
view  especially  of  the  well-kn&wn  differences  in  seed  and  the  differ- 
ences also  in  materials  of  chemical  manufacture,  each  experiment 
should  be  preceded  by  a  seed-corn  test,  made  in  the  usual  form  but 
in  a  way  to  bring  into  comparison  treated  and  untreated  seed  with 
respect  to  the  percentage  of  kernels  to  grow.  In  this  way  the  possible 
failure  of  an  experiment  and  some  loss  of  stand  may  be  prevented. 


